Bismuth-containing laser markable compositions and methods of making and using same

ABSTRACT

The present invention relates to additive, pigment or colorant materials which may be used for laser marking. The materials comprise oxides of bismuth and at least one additional metal. Preferred laser-markable bismuth-containing oxide compounds are of the formula Bi x M y O z , where M is at least one metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, Ba and Ce, x is from about 0.3 to about 70, y is from about 0.05 to about 8, and z is from about 1 to about 100. The bismuth-containing material may be dispersed in a substrate which is subsequently irradiated by a laser to provide a contrasting mark in the irradiated region.

FIELD OF THE INVENTION

The present invention relates to addition, pigment or colorant materialswhich may be used for laser marking, and more particularly relates tobismuth-containing laser markable compositions, and methods of makingand using such compositions.

BACKGROUND INFORMATION

The use of titanium dioxide as a laser markable pigment is disclosed inU.S. Pat. No. 5,091,284. However, laser marks produced from titaniumdioxide suffer from poor contrast and durability. Although manydifferent types of pigments are known, a need exists for a pigment whichcan be added to a substrate to produce high contrast durable lasermarks.

SUMMARY OF THE INVENTION

This invention relates to the use of bismuth-containing compounds as anadditive, pigment or colorant. The bismuth containing compounds areuseful in substrates comprising organic chemical compositions such asplastics, rubbers and the like, and coating compositions such as paints,printing inks and the like. The bismuth-containing compounds are alsouseful in inorganic chemical composition substrates such as glassenamels, porcelain enamels and the like. The present bismuth-containingcompounds may be used in such compositions to impart unique propertiessuch as the ability to make high contrast laser marks and/or colorchanging interactions with laser beams, unique electronic properties andhigh IR reflectance.

An aspect of the present invention is to provide a pigment of theformula Bi_(x)M_(y)O_(z), where M is at least one metal selected fromZn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca, Mg, Mo, W,Sb, Cr, Ba and Ce, x is from about 0.3 to about 70, y is from about 0.05to about 8, and z is from about 1 to about 100.

A further aspect of the present invention is to provide a laser markablecompound comprising an oxide of bismuth and at least one additionalmetal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La,Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, and Ce.

Another aspect of the present invention is to provide a laser markablesubstrate comprising a substrate material and a bismuth-containingcompound dispersed in the substrate material.

A further aspect of the present invention is to provide laser markedsubstrate comprising a substrate material, a bismuth-containing compounddispersed in the substrate material, and a laser-marked portion of thebismuth-containing compound providing a contrasting mark on thesubstrate material.

Another aspect of the present invention is to provide a method of makinga laser markable compound comprising the steps of mixing bismuth oxideor precursors thereof with at least one additional metal oxide orprecursors thereof, and heating the mixture.

A further aspect of the present invention is to provide a method ofmaking a laser markable substrate comprising dispersing abismuth-containing compound in a substrate material.

Another aspect of the present invention is to provide a method of lasermarking an article comprising providing a substrate including abismuth-containing compound and irradiating at least a portion of thesubstrate with a laser to form a marking thereon.

These and other aspects of the present invention will be more apparentfrom the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1 b are partially schematic isometric sectional viewsillustrating a process of laser marking a substrate which includes abismuth-containing composition in accordance with an embodiment of theinvention.

FIGS. 2-11 are graphs of reflectance versus wavelength for substratescomprising various bismuth-containing laser markable compositions of theinvention.

FIGS. 12-14 are graphs of reflectance versus wavelength for comparativesubstrates.

DETAILED DESCRIPTION

FIGS. 1a and 1 b schematically illustrate a laser marking operation inaccordance with an embodiment of the invention. A substrate 10 includesparticles 12 of the present bismuth-containing compounds dispersedtherein. As illustrated in FIG. 1b, a portion 14 of the substrate 10that has been irradiated with a laser beam (not shown) appears as amarking which contrasts with the unmarked portion of the substrate. Thecontrasting marked portion has different visual characteristics incomparison with the rest of the substrate, e.g., a different lightnessvalue and/or a different color value. This contrast results from theinteraction of the laser beam with the bismuth-containing compoundparticles. While not intending to be bound by theory, upon irradiation,the particles of the laser marking compounds may interact with the laserenergy by scattering, reflecting or absorbing the energy, and a chemicalreaction may occur with the substrate material, e.g., paint or plasticmaterial matrix. The reactions may occur under reducing conditions suchthat the bismuth-containing compounds change to a state of reducedoxygen content.

As used herein, the term “laser markable compound” means a compound thatcan be dispersed in a substrate and provide a contrasting mark on thesubstrate after the region has been irradiated by a laser. The resultantmarked region contrasts with the non-irradiated region, e.g., themarking may have a different lightness value and/or color value comparedwith the non-irradiated region. For example, the laser markablecompounds preferably provide contrasting marks having differentlightness values ΔL as determined by the standard CIELAB scale. Thedifference in lightness values ΔL between the marked and unmarkedregions typically has an absolute value of greater than about 10.Preferably, the absolute value of ΔL is greater than about 20, morepreferably greater than about 25. In a particularly preferredembodiment, the absolute value of ΔL is about 30 or higher.

The term “substrate” as used herein means any material in which thepresent bismuth-containing compounds may be incorporated, includingcoatings and bulk materials in various forms. The bismuth-containingcompounds may be dispersed homogeneously or non-homogeneously in thesubstrate.

The present laser markable compounds comprise Bi and at least oneadditional metal. Preferably, the compounds are oxides of Bi and theadditional metal(s), but may alternatively comprise oxide-freecompounds, hydrates, carbonates, sulfates, sulfides or other compoundscontaining the bismuth and additional metal(s). The additional metalsare preferably Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr,Ca, Mg., Mo, W, Sb, Cr, Ba and Ce.

Preferred laser markable bismuth-containing oxide compounds of thepresent invention are of the formula Bi_(x)M_(y)O_(z), where M is atleast one metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y,Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, Ba and Ce. Particularly preferredmetals include Zn, Si, Zr, Al and Sn. In this formula, x is from about0.3 to about 70, y is from about 0.05 to about 8, and z is from about 1to about 100. More preferably, x is from about 2 to about 64, y is fromabout 0.3 to about 4, and z is from about 2 to about 98. For lasermarking contrast, it has been found that higher bismuth content tends toresult in higher contrast of the mark. Preferred ratios of x/y aregreater than 2 or 3. More preferred ratios of x/y are greater than about5 or 10, more preferably greater than about 20. The bismuth-containingcompounds are typically provided in particulate form having averageparticle sizes from about 0.5 to about 40 micron, preferably from about0.8 to about 4 micron.

The bismuth-containing compounds are provided in the substrate insufficient amounts to provide laser marks of sufficient contrast.Furthermore, the compounds may be provided in sufficient amounts forcoloring purposes. The bismuth-containing compounds preferably comprisefrom about 0.1 to about 70 weight percent of the substrate, morepreferably from about 2 to about 50 weight percent.

In accordance with an embodiment of the present invention, the lasermarkable compounds are selected such that they exhibit sufficiently highcontrast laser marking qualities. The present compounds are preferablyformed by high temperature reaction of bismuth oxide and other metaloxide(s). The unique compounds are then used as a pigment type materialin the substrate, e.g., paints and plastics. By addition of thesepre-reacted unique chemical structures to the substrate compositions,the laser marking contrast properties are greatly enhanced. In preferredembodiments, the heat build-up is also greatly reduced due to unique IRreflecting properties, and electronic properties may be improved.

The bismuth-containing laser markable compounds may be made by mixing Bimetal oxides and additional metal oxides or precursors thereof, such asnitrates, carbonates, sulfates, etc, and heating the mixture andgrinding the materials. Other methods of making the laser markablecompounds include wet chemical precipitation reactions, sol gelreaction, and vapor phase reactions to make the compounds or coatings onthe surfaces of the compounds.

Various methods may be used to disperse the bismuth-containing lasermarkable compound into the substrate. For example, paints may be made byconventional mixing operations using cowles, horizontal mills, beadmills, shakers, attritors and the like. The bismuth-containing compoundsmay be mixed into plastic and other substrates using conventionalextruders, molding equipment, brabenders and the like.

Uses of the present bismuth-containing laser markable compounds includemany applications such as plastic and paint applications for theautomotive, architectural and electronics industries, and otherindustrial and military applications. One of the unique properties ofcoatings which include the present bismuth-based materials is theability to produce high contrast marks upon irradiation by a laser beam.Use of the present compounds in combination with, e.g., paint andplastic chemistries allows for extremely high contrast marks to beformed by the laser. These marks can be used for decorative oridentification purposes.

Plastic or rubber substrate compositions that can be colored and markedaccording to this invention are based upon polymeric materials that canbe natural or synthetic. Examples include natural resins, rubber,chlororubber, casein, oil-modified alkyd resins, viscose, celluloseacetate, cellulose propionate, cellulose acetobutyrate, nitrocellulose,or other cellulose ethers or esters. Synthetic organic polymers producedby polymerization, polyaddition, or polycondensation in thermosetting orthermoplastics can also be colored by this invention. Examples arepolyethylene, polystyrene, polypropylene, polyisobutylene,polyvinylchloride, polyvinylacetate, polyacrylonitrile, poly acrylicacid, other polyolefins and substituted polyolefins, as well asmethyacrylic acid esters, butadiene, as well as co polymers of the abovementioned. Examples from polyaddition and polycondensation resins arethe condensation products of formaldehyde with phenols, phenolic resins,urea, thiourea, and melamine, amino resins, polyesters, polyamides,polycarbonates, and/or silicones. These polymers can be presentindividually or as mixtures as plastic material or melts spun intofibers. They can also be dissolved as film formers or binders forlaquers, paints, or printing inks such as linseed oil, nitrocellulose,melamine resins, acrylic resins, ureaformaldehyde resins and the like.The pigmentary use of the present bismuth-containing compounds in othercoatings or materials such as carbon-carbon composites may also provideadvantages with regard to IR reflection. Also a plastic body as asubstrate which would contain the pigment (such as vinyl siding) and/orany substrate (glass, ceramic, metal, plastic, composite) having thereonan organic coating or paint which would contain and utilize the highcontrast laser markability, electronic properties, or low heat build-upproperties of the bismuth containing pigments.

Another use of the present bismuth-containing compounds is inglass-ceramic enamels for applications such as colored borders aroundglass sheets used for automobiles to enhance appearance and to preventUV degradation of underlying adhesives. Architectural, container andother glass or ceramic decorative applications where the compounds arestable and can impart desirable property improvements are also possiblein accordance with the present invention.

Glass-ceramic enamel compositions may comprise from 1 to 70 wt % of thebismuth-containing compounds, such as ZnBi₃₈O₆₀, and from 30 to 99 wt %solid glass frit compositions, or a combination of two or more frits.Additional oxide pigments may be added to the enamel compositions suchas CuCr₂O₄,(CO,Fe)(Fe,Cr)₂O₄ and the like. Printable enamel paste may bemade from 60 to 85 wt % of above solids power, plus 15 to 40 wt % of asuitable carrying vehicle or medium which can be, e.g., screen printed,roll coated or sprayed. Such glass-ceramic enamels may be applied toautomotive glass substrates, architectural glass substrates, containerglass substrates, and/or metal substrates.

The following examples are intended to illustrate various aspects of theinvention, and are not intended to limit the scope of the invention.

Bismuth Titanate Compounds

A sample designated 267-010a was made from 59.3 g Bi₂O₃ and 40.7 g TiO₂.The powders were mixed together and heated at 2,110° F. for eight hours.The sample was ground into a fine powder which had an off white orpastel yellow color. X-ray diffraction identified Bi₂Ti₄O₁₁ as the maincrystalline phase.

A sample designated 267-011a was made from 79.5 g Bi₂O₃ and 20.5 g TiO₂.The powders were mixed together and heated at 2,110° F. for eight hours.The sample was ground into a fine powder which had an off white color.X-ray diffraction identified Bi₄Ti₃O₁₂ as the main crystalline phase.

A sample designated 267-012b was made from 98.31 g Bi₂O₃ and 1.69 gTiO₂. The powders were mixed together and melted at 1832° F. for tenminutes, and then poured into water. The sample was ground into a finepowder which had an off white color. X-ray diffraction identifiedBi₁₂TiO₂₀ as the main crystalline phase.

A sample designated 267-013a was made from 97.2 g Bi₂O₃ and 2.8 g TiO₂.The powders were mixed together and melted in a crucible at 1,832° F.for ten minutes and then poured into a water bath. The sample was groundinto a fine powder which had a pastel yellow color. X-ray diffractionidentified Bi₁₂TiO₂₀ as the main crystalline phase.

Additional bismuth titanate compounds for high contrast laser markingmay include Bi₈TiO₁₄, Bi₂Ti₂O₇, Bi₂₀TiO₃₂ and other crystalline,partially crystalline and amorphous compounds.

Bismuth Ferrite Compounds

A sample designated 267-016b was made from 97.2 g Bi₂O₃ and 2.8 g Fe₂O₃.The powders were mixed together and melted in a crucible at 1,652° F.for 10 minutes, 1,832° F. for ten minutes, and then poured into a waterbath. The sample was ground into a fine powder which had a yellow-orangecolor. X-ray diffraction identified only an amorphous phase present.

Additional bismuth ferrite compounds for high contrast laser marking mayinclude Bi₂Fe₄O₉, BiFeO₃, Bi_(3.43)Fe_(0.57)O₆, Bi₂₄Fe₂O₃₉, Bi₂₅FeO₄₀,Bi₄₆Fe₂O₇₂, Bi₃₆Fe₂O₅₇ and other crystalline, partially crystalline andamorphous compounds.

Bismuth Aluminate Compounds

A sample designated 267-022a was made from 99.1 g Bi₂O₃ and 0.9 g Al₂O₃.The powders were mixed together and melted in a crucible at 1,832° F.for ten minutes, and then poured into a water bath. The sample wasground into a fine powder which had a light yellow color. X-raydiffraction identified Bi₂O₃ and Bi₂₄Al₂O₃₉ phases present.

Additional bismuth aluminate compounds for high contrast laser markingmay include AlBiO₃, Al₄Bi₂O₉, Bi₄₈Al₂O₇₅ and other crystalline,partially crystalline and amorphous compounds.

Bismuth Zirconate Compounds

A sample designated 267-024a was made from 95.7 g Bi₂O₃ and 4.3 g ZrO₂.The powders were mixed together and melted in a crucible at 1,832° F.for ten minutes, and then poured into a water bath. The sample wasground into a fine powder which had a yellow-orange color. X-raydiffraction identified Bi₂O₃, ZrO₂ and Bi₂₄Al₂O₃₉ phases present.

A sample designated 267-024b was made from 54.Og Bi₂O₃ and 46.0 g ZrO₂.The powders were mixed together and heated on a mullite plate at 1,652°F. for seven hours. The sample was ground into a fine powder which had ayellow-orange-tan color. X-ray diffraction identified Bi₂O₃, ZrO₂,Bi₁₂SiO₂₀ and SiO₂ phases present. Based on stochiometry, the expectedphase is Bi₂Zr₃O₉. However, this phase is not in the xrd computerdatabase.

A sample designated 267-024c was made from 71.6 g Bi₂O₃ and 28.4 g ZrO₂.The powders were mixed together and heated on a mullite plate at 1,652°F. for seven hours. The sample was ground into a fine powder which had ayellow-orange color. X-ray diffraction identified Bi₂O₃, ZrO₂ andBi₁₂SiO₂₀ phases present. Based on stochiometry, the expected phase isBi₄Zr₃O₁₂. However, this phase is not in the xrd computer database.

Other bismuth zirconate crystalline, partially crystalline and amorphouscompounds could be included for high contrast laser markingapplications.

Bismuth Phosphate Compounds

Bismuth phosphate compounds for high contrast laser marking may includeBiP₅O₁₄, Bi(PO₃)₃, BiPO₄, Bi₂P₄O₁₃, Bi₄P₂O₁₁, Bi₃PO₇, Bi₅PO₁₀,Bi₁₂P₂O₂₃, Bi₂₃P₄O_(44.5), Bi_(3.69)P_(0.31)O_(6.31),Bi_(7.68)P_(0.32)O_(12.32) and other crystalli amorphous compounds.

Bismuth Stannate Compounds

A sample designated 267-036a was made from 50.8 g Bi₂O₃ and 49.2 g SnO₂.The powders were ground together in water for 1.5 hour to mixthoroughly, and then dried at 220° F. Powders were heated together at1,958° F. for seven hours. The sample was ground into a fine powderwhich had a tannish off-white color. X-ray diffraction identifiedBi₂Sn₂O₇ and SnO₂ phases present.

A sample designated 267-038a was made from 99.0 g Bi₂O₃ and 1.0 g SnO₂.The powders were mixed together and melted in a crucible at 1,832° F.for twenty minutes, and then poured into a water bath. The sample wasground into a fine powder which had an orange-yellow color. X-raydiffraction identified Bi₁₂SiO₂₀ and SiO₂ phases present.

Additional bismuth stannate compounds for high contrast laser markingmay also include Bi₂Sn₃O₉, Bi₁₂SnO₂₀, Bi_(3.94)Sn_(0.06)O_(6.02),Bi₆₄SnO₉₈, Bi₇Sn_(0.1)O_(10.7) and other crystalline, partiallycrystalline and amorphous compounds.

Strontium Bismuth Oxide Compounds

A sample designated 267-047a was made from 87.8 g Bi₂O₃ and 12.9 gSrCO₃. The powders were mixed together and melted in a crucible at1,832° F. for ten minutes, 2,000° F. for ten minutes, 2,100° F. for oneminute, and then poured into a water bath. The sample was ground into afine powder which had an yellow color. X-ray diffraction identifiedcrystalline Bi₂O₃ and SrSiO₃ phases present, and an amorphous phasepresent.

Additional strontium bismuth oxide compounds for high contrast lasermarking may include Sr₆Bi₂O₉, Sr₃Bi₂O₆, Sr₂Bi₂O₅, Sr₃BiO_(5.4),Sr_(1.5)Bi_(0.5)O_(2.75), Sr_(1.2)Bi_(0.8)O₃, Sr_(0.9)Bi_(1.1)O_(2.55),Sr₃Bi₄O₉, Sr_(0.74)Bi_(1.26)O_(2.63), SrBi₂O₄,Sr_(2.25)Bi_(6.75)O_(12.38), SrBi₄O₇, Sr_(0.19)Bi_(0.81)O_(1.4),Sr_(0.16)Bi_(3.84)O_(5.92) and other crystalline, partially crystallineand amorph compounds.

Yittrium Bismuth Oxide Compounds

A sample designated 267-049a was made from 83.8 g Bi₂O₃ and 16.2 g Y₂O₃.The powders were mixed together and melted in a crucible at 1,832° F.for ten minutes and then 2,200° F. for ten minutes. The sample wasground into a fine powder which had an orangish yellow color. X-raydiffraction identified crystalline Y_(0.285)Bi_(0.715)O_(1.5) and Bi₂O₃phases present.

Additional yittrium bismuth oxide compounds for high contrast lasermarking include BiYO₃, Bi_(1.5)Y_(0.5)O₃, Bi_(06.7)Y_(0.33)O_(1.5),Bi_(1.55)Y_(0.45)O₃, Bi_(1.87)Y_(0.13)O₃, Bi_(1.9)Y_(0.1)O₃, Bi₁₉YO₃₀and other crystalline, partially crystalline and amorphous compounds.

Bismuth Niobate Compounds

A sample designated 267-059a was made from 98.8 g Bi₂O₃ and 1.2 g Nb₂O₅.The powders were mixed thoroughly together and heated in a crucible at1,832° F. for ten minutes, 2,000° F. for ten minutes, and then waterquenched. The sample was ground into a fine powder which had a slightorange color. X-ray diffraction identified crystallineBi_(5.6)Si_(0.5)O_(9.4), Bi₂O₃ and/or BiO phases as possibly beingpresent.

Additional bismuth niobate compounds for high contrast laser marking mayinclude Bi₃Nb₁₇O₄₇, Bi₂Nb₁₀O₂₈, Bi₈Nb₁₈O₅₇, BiNbO₄, Bi₅Nb₃O₁₅,Bi_(1.70)Nb_(0.30)O_(3.30), Bi₁₂Nb_(0.29)O_(18.7),Bi_(7.84)Nb_(0.16)O_(12.16) and other crystalline, partially crystallineand amorphous compounds.

Bismuth Lanthanum Oxide Compounds

A sample designated 267-063a was made from 48.8 g Bi₂O₃ and 51.2 gLa₂O₃. The powders were mixed thoroughly by wet milling together in analumina mill and media and then dried at 220° F. The sample was heatedon a mullite plate at 1,742° F. for twenty four hours and then airquenched. The sample was ground into a fine powder which had a yelloworange color. X-ray diffraction identified crystalline BiLa₂O_(4.5) andBi₈La₁₀O₂₇ phases as being present.

Additional bismuth lanthanum oxide compounds for high contrast lasermarking may include Bi_(0.92)La_(1.08)O_(3.03), Bi_(0.4)La_(0.6)O_(1.5),BiLa₂O_(4.5) and other crystalline, partially crystalline and amorphouscompounds.

Bismuth Tantalum Oxide Compounds

A sample designated 267-064a was made from 97.6 g Bi₂O₃ and 2.4 g Ta₂O₅.The powders were mixed thoroughly by wet milling together in an aluminamill and media and then dried at 220° F. The sample was heated on amullite plate at 1,418° F. for twenty-four hours and then air quenched.The sample was ground into a fine powder which had a yellow orangecolor. X-ray diffraction identified crystallineBi_(7.8)Ta_(0.2)O_(12.20) as a major phase and Bi₂O₃, Bi₂₄Al₂O₃₉ andSiO₂ minor phases as being present.

Additional bismuth tantalum oxide compounds for high contrast lasermarking may include Bi_(3.0)TaO_(7.0), BiTaO₄, BiTa₇O₁₉ and othercrystalline, partially crystalline and amorphous compounds.

Bismuth Praseodymium Oxide Compounds

A sample designated 267-068a was made from 74.6 g Bi₂O₃ and 25.4 gPr₂O₃. The powders were mixed thoroughly and then heated on a mulliteplate at 1,565° F. for five hours and then quenched in liquid nitrogen.The sample was ground into a fine powder which had a yellow green color.X-ray diffraction identified crystalline Bi_(1.35)Pr_(0.65)O₃ as a majorphase and Bi₂O₃ and SiO₂ minor phases as being present.

A sample designated 267-068b was made from 94.7 g Bi₂O₃ and 5.3 g Pr₂O₃.The powders were mixed thoroughly and then heated on a mullite plate at1,490° F. for five hours and then quenched in liquid nitrogen. Thesample was ground into a fine powder which had a yellowish tan color.X-ray diffraction identified crystalline Bi_(1.854)Pr_(0.146)O₃ as amajor phase and Bi₂O₃ and Bi₁₂SiO₂₀ minor phases as being present.

A sample designated 267-069a was made from 96.5 g Bi₂O₃ and 3.5 g Pr₂O₃.The powders were mixed thoroughly and then heated on a mullite plate at1,454° F. for five hours and then quenched in liquid nitrogen. Thesample was ground into a fine powder which had a yellowish tan color.X-ray diffraction identified crystalline Bi_(1.904)Pr_(0.096)O₃ as amajor phase and Bi₂O₃ and Bi₁₂SiO₂₀ minor phases as being present.

Additional bismuth praseodymium oxide compounds for high contrast lasermarking may include other crystalline, partially crystalline, andamorphous compounds.

Bismuth Calcium Oxide Compounds

A sample designated 267-075a was made from 90.3 g Bi₂O₃ and 9.7 g CaCO₃.The powders were mixed thoroughly and the sample was heated on a mulliteplate at 1,562° F. for seven hours and then air quenched. The sample wasground into a fine powder which had a yellow orange-brown color. X-raydiffraction identified Bi₂O₃, Bi₂₄Al₂O₃₉, Ca(OH)₂ andBi_(1.6)Ca_(0.4)O_(2.8) phases as being present.

Additional bismuth calcium oxide compounds for high contrast lasermarking may include Bi₆Ca₇O₁₆, Bi₂Ca₂O₅, Bi_(1.09)Ca_(0.91)O_(2.55),Bi₁₀Ca₇O₂₂, Bi₆Ca₄O₁₃, Bi₂CaO₄, Bi₁₄Ca₅O₂₆, Bi_(3.11)Ca_(0.89)O_(5.56),Bi_(1.6)Ca_(0.4)O_(2.8) and other crystalline, partially crystalline andamorphous compounds.

Bismuth Zinc Oxide Compounds

A sample designated 174-115e was made from 97.7 g Bi₂O₃ and 2.3 g ZnO.The powders were mixed thoroughly and the sample was heated in acordierite sagger at 1,380° F. for sixty-five hours. The sample wasground into a fine powder which had an off white color. X-raydiffraction identified the ZnBi₃₈O₆₀ phase as being present.

Additional bismuth zinc oxide compounds for high contrast laser markingmay include Bi₄₈ZnO₇₃, Bi_(7.65)Zn_(0.35)O_(11.83), BiZn₃₈O₅₈ and othercrystalline, partially crystalline and amorphous compounds.

Bismuth Silicate Compounds

A sample designated 174-115c was made from 97.9 g Bi₂O₃ and 2.1 g SiO₂.The powders were mixed thoroughly and the sample was heated in acordierite sagger at 1,530° F. for fourteen hours. The sample was groundinto a fine powder which had an off white color. X-ray diffractionidentified Bi₁₂SiO₂₀, Bi₂O₃ and Bi₂SiO₅ phases as being present.

Additional bismuth silicate compounds for high contrast laser markingmay include Bi₄Si₃O₁₂ and other crystalline, partially crystalline andamorphous compounds.

In addition to the above-noted compounds, bismuth cuprate compounds forhigh contrast laser marking may include Bi₂CuO₄ and other crystalline,partially crystalline and amorphous compounds.

Alternatively, bismuth magnesium oxide compounds for high contrast lasermarking may include Bi₁₂MgO₁₉, Bi₁₈Mg₈O₃₆ and other crystalline,partially crystalline and amorphous compounds.

Bismuth-containing compounds, such as those described in the precedingexamples, may be used in accordance with the present invention toproduce laser marks on or in various types of substrates. A selectedportion of the substrate comprising the bismuth-containing compound isirradiated with a beam to form a permanent marking therein or thereon.For many types of markings, the irradiated portion of the substratesurface may comprise from about 0.1 to about 99 percent of the totalsurface area of the substrate, typically from about 1 to about 95percent. A laser is preferably used to selectively irradiate thesubstrate. However, other forms of focused energy may be used inaccordance with the present invention. Irradiation may be achieved bymoving a laser beam over a stationary substrate using conventional beamsteering methods, by moving the substrate in relation to the laser beamand/or by masking the substrate. Laser irradiation is typically achievedby directing the beam directly against the surface of the substrate tobe marked, but may also be achieved by directing the beam through therear side of a sufficiently transparent substrate.

Suitable lasers for use in accordance with the present invention includeneodymium:yttrium aluminum garnet (Nd:YAG) lasers, carbon dioxide (CO₂)lasers, diode lasers, excimer lasers and the like.

Typical YAG lasers emit light in the near-infrared spectrum atwavelengths of 1064 nm. Such lasers typically have continuous poweroutputs of from about 1 to about 50 watts, and can be operated in apulsed mode at typical peak powers of from about 1 watt to about 45kilowatts. For pulsed mode operation, frequencies of from about 1 toabout 64,000 pulses/second may be used.

Typical CO₂ lasers emit light in the far-infrared region of thespectrum, with intensity spikes at wavelengths of 9.8 and 10.6 microns.Such CO₂ lasers typically operate at a continuous output power of fromabout 1 to about 40 watts.

In accordance with the present invention, the size of the laser spotthat impinges the substrate is typically greater than 0.1 micron indiameter, preferably from about 40 to about 500 microns, and morepreferably from about 50 to about 125 microns. The speed at which thelaser beam travels across the surface of the substrate preferably rangesfrom 0 to about 100 inches/second (up to about 250 cm/second), morepreferably from about 1 or 2 to about 20 inches/second (about 2.5 or 5to 50 cm/second) for most thicknesses and compositions. The laser beammay be projected with a seam overlap of 0 to 100 percent, preferablyfrom about 10 to about 90 percent for many applications. The laserparameters are controlled in order to provide sufficient localizedheating of the bismuth-containing compound, while avoiding unwanteddamage to the substrate.

The laser beam, the movement of which can be controlled by a computer,may be used to create discrete symbols or designs or, alternatively, maybe serially indexed across the surface of the substrate to createmultiple symbols or designs at the same time. For example, a word may becreated by separately making each letter of the word with the laser, orby rastering the laser across the entire word to form all of the lettersat the same time. A single laser beam may be used for marking inaccordance with the present invention. Alternatively, two or more laserbeams may be used.

During the irradiation step, the surface of the substrate may be exposedto any desired type of atmosphere. For example, the atmosphere maycomprise air at atmospheric, sub-atmospheric or super-atmosphericpressures. Furthermore, the atmosphere may comprise an inert gas such asnitrogen, argon or carbon dioxide, an oxidizing atmosphere such as airor oxygen, a reducing atmosphere such as hydrogen or carbon monoxide, ora vacuum. Oxidizing or reducing gases can be used in a combination withinert gases.

Laser marking tests were performed using several bismuth-containingcompounds of the present invention. The following application and lasermarking procedures were used in laser marking tests.

Enoxy Coating Test

Waterbased epoxy (Sherwin Williams Hydralon B)—50 g

Bismuth-containing pigment—10 g

Defoamer (Byk 023)—0.05 g

Glass beads—50 g

Shake for 30 minutes; filter the dispersion; add one part hardener(Sherwin Williams KEM Aqua Hydralon B) to 2 parts of the dispersion;produce a film with the finished paint on an aluminum panel and let airdry overnight; mark the film surface with YAG or CO₂ laser to producehigh contrast marks; and measure the contrast between the unmarked andmarked surfaces with a spectrophotometer.

Plastic Test

Thermoplastic polyurethane resin (Bayer 795 U)—195 g

Bismuth-containing pigment—5 g

Shake for 2 minutes; injection mold the samples with a standardinjection molding machine at 395° F. into color chips; mark the chipswith YAG or CO₂ laser to produce high contrast marks; and measure thecontrast between the unmarked and marked surfaces with aspectrophotometer.

For YAG laser marking, the following parameters were used: 10,000pulses/second; 20 inches per second; 32 amps power; 0.005 dot size; and40 percent seam overlap. For CO₂ laser marking, the following parameterswere used: 50 percent of 35 watt power; 36 inches/minute; and 500 dpi.

Table 1 lists the color values of each epoxy coating sample before andafter laser marking. The standard CIELAB L*a*b* system was used todefine the color of the samples. The L*value refers to the lightness ofthe sample, with L*=100 designating the lightness upper limit and L*=0designating the darkness lower limit.

The a*value describes the red or green value of the pigment, with apositive a*value designating red, and a negative a*value designatinggreen. The b*value represents the blue or yellow value, with a positiveb*value designating yellow and a negative b*value designating blue. TheΔL*, Δa*and Δb*values represent the difference in the L*, a*and b*valuesbetween the unmarked and marked samples. The ΔE*values are a measure ofthe combined difference in lightness and color values between theunmarked and marked samples.

TABLE 1 Epoxy Coating Laser Mark Contrast Sample ID L* a* b* ΔL* Δa* Δb*ΔE* White 87.88 −0.36 4.38 267-010A 267-010A 62.45 1.51 6.39 −25.43 1.872.00 25.58 Marked White 89.99 −0.22 4.40 267-101A′ 267-010A′ 63.86 1.466.22 −26.13 1.67 1.82 26.25 Marked White 87.87 −0.97 7.89 267-011A267-011A 60.66 1.71 7.45 −27.21 2.68 −0.44 27.35 Marked Light 86.24−5.59 18.96 Yellow 267-12B 267-12B 53.42 2.07 9.08 −32.82 7.67 −9.8735.12 Marked Light 88.25 −5.52 23.19 Yellow 267-013A 267-013A 54.20 1.869.64 −34.05 7.37 −13.56 37.38 Marked Yellow 77.48 2.78 46.39 267-016B267-016B 53.73 2.03 21.98 −23.76 −0.76 −24.41 34.07 Marked Yellow 85.76−7.82 21.46 267-022A 267-022A 58.75 −1.66 14.00 −27.01 6.15 −7.46 28.69Marked Yellow 86.37 −6.44 38.04 267-024A 267-024A 47.96 1.57 13.03−38.41 8.01 −25.01 46.53 Marked Light 87.57 −3.30 13.46 Yellow 267-038A267-038A 57.84 1.36 9.28 −29.72 4.66 −4.17 30.38 Marked Light 89.05−5.66 13.68 Yellow 267-047A 267-047A 53.03 2.07 6.73 −36.02 7.73 −6.9637.49 Marked Yellow 84.46 −5.38 36.02 267-049A 267-049A 60.62 −1.1919.56 −23.84 4.19 −16.45 29.27 Marked Light 87.99 −8.25 22.84 Yellow267-059A 267-059A 52.12 0.01 11.73 −35.87 8.26 −11.11 38.45 Marked White88.80 −2.39 8.38 174-115E 174-115E 49.80 2.78 6.91 −38.99 5.17 −1.4739.36 Marked White 86.34 −1.17 4.38 174-115C 174-115C 53.00 2.06 2.68−33.34 3.22 −1.71 33.54 Marked White 95.46 −0.99 2.23 R960 R960 91.38−0.89 2.47 −4.07 0.10 0.24 4.08 Marked

The results listed in Table 1 illustrate the high contrast between themarked and unmarked epoxy coating samples incorporating thebismuth-containing compositions, in comparison with a coating samplecontaining a standard TiO₂ pigment designated R960 in Table 1. The ΔLvalues from the samples comprising the present bismuth-containingcompositions are over 20, and in many cases over 30.

Table 2 lists the color values of each plastic sample before and afterlaser marking.

TABLE 2 Plastic Laser Mark Contrast Sample ID L* a* b* ΔL* Δa* Δb* ΔE*179-115E 81.0 −0.75 11.58 Unmarked 179-115E 38.5 1.63 4.12 −42.46 2.38−7.46 43.18 Marked 267-010A 84.1 1.03 9.87 Unmarked 267-010A 56.9 1.886.62 −27.16 0.85 −3.25 27.37 Marked 267-010A′ 83.2 1.54 10.12 Unmarked267-010A′ 59.3 2.00 6.81 −23.88 0.46 −3.31 24.12 Marked 267-011A 86.7−0.18 10.78 Unmarked 267-011A 52.5 2.01 6.05 −34.25 2.19 −4.73 34.65Marked 267-012B 81.5 −3.71 20.64 Unmarked 267-012B 36.9 2.28 4.48 −44.625.99 −16.16 47.83 Marked 267-013A 86.1 −5.16 23.18 Unmarked 267-013A48.2 1.11 6.80 −37.89 6.27 −16.38 41.75 Marked 267-016B 75.9 4.11 45.11Unmarked 267-016B 42.8 1.34 7.95 −33.14 −2.77 −37.16 49.87 Marked267-022A 83.3 −5.38 23.76 Unmarked 267-022A 37.8 2.23 4.28 −45.51 7.61−19.48 50.08 Marked 267-024A 82.9 4.05 35.10 Unmarked 267-024A 35.2 2.043.46 −47.68 6.09 −31.64 57.54 Marked 267-038A 86.0 −2.08 15.55 Unmarked267-038A 44.0 1.29 2.89 −42.04 3.37 −12.66 44.03 Marked 267-047A 85.8−3.57 14.99 Unmarked 267-047A 49.6 0.96 6.40 −36.19 4.53 −8.59 37.47Marked 267-049A 84.6 −3.55 37.92 Unmarked 267-049A 50.2 −0.21 10.58−34.37 3.33 −27.34 44.04 Marked 267-059A 87.1 −6.67 27.10 Unmarked267-059A 41.8 1.48 4.40 −45.29 8.15 −22.70 51.31 Marked

The results listed in Table 2 illustrate the high contrast between themarked and unmarked plastic samples incorporating the bismuth-containingcompositions. The ΔL values are greater than 20, and most are over 30 or40.

In accordance with an embodiment of the present invention, anadvantageous property of the compounds is good infrared reflectance.These infrared reflective properties were tested versus various othercommercial pigments, and the measurements have shown that the presentcompositions exhibit low heat buildup properties. Thus, for reduced heatbuild-up in applications such as architectural, military, marine vesselpaint, automotive paint and vinyl siding applications, the presentbismuth-containing compounds have a very wide use potential.

In order to demonstrate the visible and IR reflectance characteristicsof the present bismuth-containing materials, some of the epoxy coatingsamples listed in Table 1 were tested for reflectance at wavelengths offrom 300 to 2,500 nm. Graphs 15 showing reflectance versus wavelengthdata for some of the epoxy coating samples are provided in FIGS. 2-11.Comparison curves for similar epoxy samples containing conventionalTiO₂, 10401 (NiSbTi), and 10408 (CrSbTi) pigments are provided in FIGS.12-14. Favorable IR reflectance properties are achieved by the presentbismuth-containing compounds.

The heat build-up results of a number of the synthesized compounds arelisted below.

TABLE 3 Heat Build-Up Results Sample Ta Tm ΔTlu ΔTv ΔTh Carbon Black72.3 216.1 143.8 R960 TiO2 73.3 134.6 61.3 4.61 56.1 267-010-A 73.5135.9 62.4 46.5 56.6 267-010-A 73.4 138.9 65.5 47.5 57.8 267-011-A 72.9138.1 65.2 47.3 57.5 174-115-E 73.3 140.2 66.9 48 58.4 267-012-B 73.2140.3 67.1 48 58.4 267-016-B 72.8 139.7 66.9 47.8 58.2 10401 NiSbTi 72.9136.9 64 46.9 57.1 10408 CrSbTi 73 138.9 65.9 47.6 57.8 Ta = ambient airtemperature in the lab Tm = maximum temperature of specimen ΔTlu = Tm-TaΔT = ΔTlu/ΔTlb * ΔTh (or ΔTv) ΔTlu = temperature rise above ambienttemperature ΔTv = for vertical position 74 degrees F. ΔTh = for verticalposition 90 degrees F.

Table 3 illustrates low heat build up properties for the darker colorshades, which is comparable to the lighter TiO₂. Comparable IRreflectance performance is also shown in Table 3 for the presentbismuth-containing compounds in comparison with standard 10401 and 10408pigments used in the vinyl siding industry, which are known to be goodfor IR reflecting and heat build-up.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

What is claimed is:
 1. A pigment of the formula Bi_(x)M_(y)O_(z), whereM is at least one metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr,Si, Y, Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Ba, and Ce, x is from 0.3 toabout 70, y is from about 0.05 to about 8, z is from about 1 to about100, and the ratio of x to y is greater than
 2. 2. The pigment of claim1, wherein the ratio of x to y is greater than
 5. 3. The pigment ofclaim 1, wherein the ratio of x to y is greater than
 10. 4. The pigmentof claim 1, wherein the ratio of x to y is greater than
 20. 5. Thepigment of claim 1, wherein M comprises Zn, Si, Zr, Al or Sn.
 6. Thepigment of claim 1, wherein the pigment is markable by a laser.
 7. Alaser markable compound of the formula Bi_(x)M_(y)O_(z), wherein Mcomprises Zn, Si, Zr, Al, or Sn, and x is from about 0.3 to about 70, yis from about 0.05 to about 8 and z is from about 1 to
 100. 8. The lasermarkable compound of claim 7, wherein the ratio of x to y is greaterthan
 2. 9. The laser markable compound of claim 7, wherein the ratio ofx to y is greater than
 5. 10. The laser markable compound of claim 7,wherein the ratio of x to y is greater than
 10. 11. A laser markablesubstrate comprising: a substrate material; and a bismuth-containingcompound dispersed in the substrate material, wherein thebismuth-containing compound comprises an.oxide of bismuth and at leastone additional metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr,Si, Y, Nb, La, Ta, Pr, Ca and Mg.
 12. The laser markable substrate ofclaim 11 wherein the bismuth-containing compound comprises the formulaBi_(x)M_(y)O_(z), where M is at least one metal selected from Zn, Ti,Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca and Mg, x is fromabout 0.3 to about 70, y is from about 0.05 to about 8, and z is fromabout 1 to
 100. 13. The laser markable substrate of claim 12, whereinthe ratio of x to y is greater than
 2. 14. The laser markable substrateof claim 12, wherein the ratio of x to y is greater than
 5. 15. Thelaser markable substrate of claim 12, wherein the ratio of x to y isgreater than
 10. 16. The laser markable substrate of claim 12 wherein Mcomprises Zn, Si, Zr, Al or Sn.
 17. The laser markable substrate ofclaim 11, wherein the bismuth-containing compound comprises from about0.1 to about 70 weight percent of the substrate.
 18. The laser markablesubstrate of claim 11, wherein the bismuth-containing compound comprisesfrom about 2 to about 50 weight percent of the substrate.
 19. A methodof making a laser markable compound comprising: mixing bismuth oxide orprecursors thereof with at least one additional metal oxide orprecursors thereof; and heating the mixture, wherein the compoundcomprises the formula Bi_(x)M_(y)O_(z), where M is at least one metalselected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr,Ca, Mg, Mo, W, Sb, Ba and Ce, x is from about 0.3 to about 70, y is fromabout 0.05 to about 8, and z is from about 1 to 100 and the ratio of xto y to greater then z.
 20. A method of making a laser markablesubstrate comprising dispersing a bismuth-containing compound in asubstrate material, wherein the bismuth-containing compound comprisesthe formula Bi_(x)M_(y)O_(z), where M is at least one metal selectedfrom Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca, Mg,Mo, W, Sb, Ba and Ce, x is,from about 0.3 to about 70, y is from about0.05 to about 8, and z is from about 1 to and the ratio of x to y togreater then z.